Sensor controller, position indicator, and position detecting system

ABSTRACT

A sensor controller is provided for use in a position detector for detecting a position of a position indicator on a touch surface. The sensor controller includes a microprocessor for outputting a value of a symbol to be sent to the position indicator. The sensor controller includes a transmitter coupled to the microprocessor for generating a transmission signal including a chip string CN1 produced by cyclically shifting a code string PNa having autocorrelation characteristics by a shift quantity based on the value of the symbol to be sent, and sending the generated transmission signal to the position indicator via the touch surface. A higher bit rate can be obtained for a given chip rate compared with the prior art in which only 1 bit can be expressed by one code string.

BACKGROUND Technical Field

The present disclosure relates to a sensor controller, a positionindicator, and a position detecting system, and more particularly to asensor controller for use in a position detector that detects theposition of a position indicator on a touch surface, a positionindicator capable of receiving signals sent by such a position detector,and a position detecting system that is provided with such a positiondetector and a position indicator.

Description of the Related Art

There is known a position detecting system, in which bidirectionalcommunication is performed between a position indicator as a pen-typedevice and a position detector as a device having a touch surface suchas a tablet or the like, or in which unidirectional communication iscarried out from the position detector to the position indicator. PatentDocument 1 discloses an example of the latter position detecting system.

Patent Document 2 discloses use of the direct sequence spread spectrum(DSSS) technique (hereinafter described as “direct spread technique”)for communication between a position indicator and a position detectorthat make up a position detecting system.

PRIOR ART DOCUMENT Patent Documents

Patent Document 1: PCT Patent Publication No. WO2015/111159

Patent Document 2: U.S. Pat. No. 7,084,860

BRIEF SUMMARY Technical Problems

A communication method that is resistant to noise can be realized byusing a direct spread technique for a method of communication between aposition indicator and a position detector, as is the case with thedisclosure described in Patent Document 2.

For example, a transmission-side device can be configured to encode aplurality of bits (a transmission bit string) that make up transmissiondata, bit by bit, using a known code string having autocorrelationcharacteristics (a code string where a peak correlation value appearsonly at a shift quantity 0 when a correlation value is calculatedbetween the code string and a code string produced by cyclicallyshifting the code string or its inverted signal by an arbitrary shiftquantity).

FIG. 16 depicts an example of a chip string generated by thetransmission-side device according to an encoding process. In theexample depicted in FIG. 16, “00010010111” having a length of 11 chipsis used as the known code string having autocorrelation characteristics.A transmission bit string is given as “10110.” As depicted in FIG. 16,if a bit to be sent has a value of “1,” then the above code stringdirectly becomes a transmission chip string. On the other hand, if a bitto be sent has a value of “0,” then an inverted code string from theabove code string becomes a transmission chip string.

When a reception-side device receives the transmission chip string sentby the transmission-side device, the reception-side device inputs thechip string, chip by chip, successively into a first-in, first-out shiftregister that has a capacity of 11 chips, and calculates on each inputoccasion a correlation value between a chip string of 11 chipstemporarily accumulated in the shift register and the above known codestring. Since the code string has autocorrelation characteristics, thecalculated correlation value is a maximum value (+11 in this example)when the chip string stored in the shift register is precisely“00010010111,” and a minimum value (−11 in this example) when the chipstring stored in the shift register is precisely “11101101000” (aninverted code string from the known code string). On the other hand, thecorrelation values for other chip string values are values close to 0(+1 or −1 in this example). The reception-side device is configured toextract transmission data sent by the transmission-side device from thereceived chip string, using such features of correlation values.

However, the communication method using the above direct spreadtechnique suffers from a problem that it is difficult to obtain a highbit rate. Specifically, in the example depicted in FIG. 16, since 11chips are required to express one bit (two values), only a value of 1/11of the chip rate can be achieved as a bit rate. As it is not easy toincrease the chip rate, it is difficult to obtain a high bit rate as aresult.

Consequently, one aspect of the present disclosure is directed toproviding a sensor controller, a position indicator, and a positiondetecting system which are able to obtain a high bit rate compared withthe background art.

Technical Solution

A sensor controller according to an aspect of the present disclosure isa sensor controller for use in a position detector for detecting aposition of a position indicator on a touch surface. The sensorcontroller includes a controller that outputs a value of a symbol to besent to the position indicator. The sensor controller includes atransmitter that generates a transmission signal including a first chipstring produced by cyclically shifting a spread code havingautocorrelation characteristics by a shift quantity based on the valueof the symbol to be sent, and sends the generated transmission signal tothe position indicator via the touch surface.

A position indicator according to the aspect of the present disclosureis a position indicator configured to be able to receive a signal sentby a sensor controller through a position detector having a touchsurface. The position indicator includes a receiver that receives asignal, demodulates the value of a symbol included in the signal basedon a cyclic shift quantity for a code string having autocorrelationcharacteristics which is included in the signal, and restores a sentcommand based on the demodulated value of the symbol. The positionindicator includes a controller that controls the transmission of asignal to the sensor controller based on the command.

A position detecting system according to the aspect of the presentdisclosure is a position detecting system including a position indicatorand a position detector for detecting a position of the positionindicator on a touch surface. The position detector includes acontroller for outputting a value of a symbol to be sent to the positionindicator, and a transmitter for generating a transmission signalincluding a first chip string produced by cyclically shifting a codestring having autocorrelation characteristics by a shift quantity basedon at least a portion of the value of the symbol to be sent, and sendingthe generated transmission signal to the position indicator via thetouch surface. The position indicator includes a receiver forsuccessively inputting a series of chips generated by receiving thetransmission signal to a first-in, first-out shift register, and eachtime a chip is input, calculating correlation values between the chipstring temporarily accumulated in the shift register and a plurality ofcode strings produced by cyclically shifting a predetermined code stringhaving autocorrelation characteristics by an arbitrary shift quantity,thereby detecting a bit string included in the series of chips.

Advantageous Effects

According to the present disclosure, since the cyclic shifting of a codestring is used in generating a chip string, it is possible to express 2bits or more with one code string. Accordingly, it is possible to obtaina high bit rate at the same chip rate, compared with the background artwhere only 1 bit can be expressed by one code string.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram depicting an arrangement of a position detectingsystem 1 according to an embodiment of the present disclosure.

FIG. 2 is a diagram depicting an arrangement of a position detector 3depicted in FIG. 1.

FIGS. 3A through 3C are diagrams depicting examples of signals generatedby a spread processor 63.

FIG. 4 is a block diagram depicting functional blocks of a circuit unit24 depicted in FIG. 1.

FIG. 5 is a timing chart illustrative of a chronological sequence ofoperation of a stylus 2 and a sensor controller 31 depicted in FIG. 1.

FIG. 6 is a block diagram depicting functional blocks of the spreadprocessor 63 depicted in FIG. 2.

FIG. 7 is a block diagram depicting functional blocks of a controlcircuit 63 a depicted in FIG. 6.

FIG. 8 is a diagram illustrative of a chip string CN2 output from ashift register 63 d depicted in FIG. 6.

FIG. 9A is a diagram depicting a solid-line curve that representscorrelation values between a code string C1-0 depicted in FIG. 8 and acode string produced by cyclically shifting a portion, except a fixedchip NRa, of the code string C1-0 by an arbitrary shift quantity, and abroken-line curve that represents correlation values between a spreadcode PN depicted in FIG. 6 and a code string produced by cyclicallyshifting the spread code PN by an arbitrary shift quantity. FIG. 9B is adiagram depicting a solid-line curve that represents correlation valuesbetween the code string C1-0 depicted in FIG. 8 and a code stringproduced by cyclically shifting a portion, except the fixed chip NRa, ofan inverted code from the code string C1-0 by an arbitrary shiftquantity, and a broken-line curve that represents correlation valuesbetween the spread code PN depicted in FIG. 6 and a code string producedby cyclically shifting an inverted code from the spread code PN by anarbitrary shift quantity.

FIG. 10 is a diagram depicting an example of a second control signalUS_c2.

FIG. 11 is a block diagram depicting functional blocks of a correlatingcircuit 26 b depicted in FIG. 4.

FIG. 12 is a diagram illustrative of a chip string CN2 output from theshift register 63 d depicted in FIG. 6 according to a first modificationof the embodiment of the present disclosure.

FIG. 13 is a diagram illustrative of a chip string CN2 output from theshift register 63 d depicted in FIG. 6 according to the firstmodification of the embodiment of the present disclosure.

FIG. 14 is a block diagram depicting functional blocks of a correlatingcircuit 26 b according to a second modification of the embodiment of thepresent disclosure.

FIG. 15 is a timing chart illustrative of a chronological sequence ofoperation of a stylus 2 and a sensor controller 31 according to a thirdmodification of the embodiment of the present disclosure.

FIG. 16 is a diagram depicting an example of a transmission code stringgenerated by a position detector according to the background art of thepresent disclosure.

DETAILED DESCRIPTION

An embodiment of the present disclosure will be described in detailbelow with reference to the accompanying drawings.

FIG. 1 is a diagram depicting an arrangement of a position detectingsystem 1 according to an embodiment of the present disclosure. Theposition detecting system 1 is provided with a stylus 2 and a positiondetector 3.

The stylus 2 is a position indicator of the active ES (electrostatic)type configured to be able to receive signals that are successively sentby the position detector 3. As depicted in FIG. 1, the stylus 2 has acore 20, an electrode 21, a pen pressure detection sensor 23, a circuitunit 24, and a power supply 25. A cylindrical AAAA cell, for example, isused as the power supply 25. In the present embodiment, an example inwhich the present disclosure is applied to the stylus 2 of the active EStype will be described. However, the present disclosure is also suitablyapplicable to a stylus of another type such as the electromagneticinduction type, for example.

The core 20 is a rod-shaped member disposed such that its longitudinaldirection is aligned with the pen axis direction of the stylus 2. Thecore 20 has a distal end 20 a whose surface is coated with anelectrically conductive material, providing the electrode 21. The core20 has a proximal end held against the pen pressure detection sensor 23.The pen pressure detection sensor 23 is used to detect a pressure (penpressure) applied to the distal end 20 a of the core 20.

The circuit unit 24 has a function to receive uplink signals US (a firstcontrol signal US_c1 and a second control signal US_c2) sent by theposition detector 3 through the electrode 21, and a function to senddownlink signals DS (a position signal DS_pos and a data signal DS_res)through the electrode 21 to the position detector 3. These signals willbe described in detail later.

The position detector 3 has a sensor 30 that provides a touch surface 3a, a sensor controller 31, and a host processor 32 that controls variousparts of the position detector 3 which include the sensor 30 and thesensor controller 31.

The sensor controller 31 has a function to receive the downlink signalsDS (the position signal DS_pos and the data signal DS_res) sent by thestylus 2 through the sensor 30, and a function to send the uplinksignals US (the first control signal US_c1 and the second control signalUS_c2) through the sensor 30 to the stylus 2.

FIG. 2 is a diagram depicting an arrangement of the position detector 3.As depicted in FIG. 2, the sensor 30 includes a matrix of line-shapedelectrodes 30X and line-shaped electrodes 30Y, and is capacitivelycoupled to the stylus 2 through the line-shaped electrodes 30X, 30Y. Thesensor controller 31 has a transmitter 60, a selecting section 40, areceiver 50, a logic unit 70, and an MCU 80 (controller).

The transmitter 60 is a circuit for sending the uplink signals US (thefirst control signal US_c1 and the second control signal US_c2) depictedin FIG. 1. Specifically, the transmitter 60 includes a first controlsignal supply section 61, a switch 62, a spread processor 63, a codestring hold section 64, and a transmission guard section 65. Of thesecomponents, the first control signal supply section 61 will be describedas being included in the transmitter 60 according to the presentembodiment. However, the first control signal supply section 61 may beincluded in the MCU 80.

The first control signal supply section 61 holds a detection pattern c1,and has a function to repeatedly output a signal (or a bit string)corresponding to the detection pattern c1 successively during asuccessive transmission period TCP (e.g., 3 msec.)

depicted in FIG. 5 to be described later, as instructed by a controlsignal ctrl_t1 supplied from the logic unit 70. The first control signalsupply section 61 also has a function to output a predetermineddelimiter pattern STP successively at least twice immediately after theend of the successive transmission period TCP or at the time of startingto send the second control signal US_c2. The first control signal US_c1is made up of the detection pattern c1 and the delimiter pattern STPthus output from the first control signal supply section 61.

The detection pattern c1 is a pattern of the values of symbols used forthe stylus 2 to detect the existence of the sensor controller 31, and isknown to the stylus 2 in advance (before the stylus 2 detects the sensorcontroller 31). A symbol is a unit of information used for modulation ina transmission process (a unit of information represented by atransmission signal), and a unit of information obtained by demodulatingone symbol as a reception signal in a reception process. The values ofsymbols may include a value that is converted into a bit string by thestylus 2 having received the symbol (hereinafter described as “bitstring associated value”) and a value that is not converted into a bitstring (hereinafter described as “bit string unassociated value”). Asdepicted in Table 1 to be described later, a symbol corresponding to theformer value may take one of values, wherein a total number of suchvalues is indicated by a power of 2, and is associated with a bitstring, such as “0001.” The bit length of each symbol represented by abit string is determined by the specifications of the spread processor63. On the other hand, a symbol corresponding to the latter value takesone or more (e.g., two) values not associated with a bit string, such as“P” and “M” as depicted in Table 1 to be described later. According toan example depicted in Table 1 to be described later, “P” and “M” areassociated respectively with a predetermined spread code string and aninverted code string.

The detection pattern c1 can be represented by a pattern of bit stringunassociated values, and may include a repetition of two bit stringunassociated values “P” and “M,” such as “PMPMPM . . . ,” for example.

The delimiter pattern STP is a pattern of symbols for notifying thestylus 2 of the end of the successive transmission period describedabove, and includes a pattern of symbols that does not appear in therepetition of the detection pattern c1. For example, if the detectionpattern c1 includes a repetition of two bit string unassociated values“P” and “M,” such as “PMPMPM . . . ,” then the delimiter pattern STP mayinclude a pattern “PP” made up of two consecutive bit train unassociatedvalues “P.” The delimiter pattern STP and the detection pattern c1 maybe switched around such that the delimiter pattern STP includes apattern “PM” and the detection pattern c1 includes a pattern “PP.”

The switch 62 has a function to select either the first control signalsupply section 61 or the MCU 80 based on a control signal ctrl_t2supplied from the logic unit 70, and supply an output signal from theselected one to the spread processor 63. If the switch 62 selects thefirst control signal supply section 61, then the spread processor 63 issupplied with the detection pattern c1 or the delimiter pattern STP. Ifthe switch 62 selects the MCU 80, then the spread processor 63 issupplied with control information c2.

The control information c2 includes information including a command thatrepresents the content of an instruction for the stylus 2, and isgenerated by the MCU 80 and sent on the second control signal US_c2 asdepicted in FIG. 10. The control information c2 includes values (forexample, 0 through 15) of symbols associated with a variable-length bitstring, and is different from the detection pattern c1 in that itsvalues are not shared with the stylus 2 in advance. The controlinformation c2 is different from the detection pattern c1 that includesthe values “P” and “M” in that it is indicated by value “D” that cantake any one of a number of values (e.g., 8 values, 16 values) that canbe indicated by a power of 2 having a predetermined bit length describedabove. As depicted in FIG. 10, the second control signal US_c2 includesa delimiter pattern STP “PP” as a preamble followed by a transmissionsignal (chip string) corresponding to three items of control informationc2 which are indicated by D1 through D3.

The code string hold section 64 has a function to generate and hold aspread code PN (second code string) which is 11 chips long that hasautocorrelation characteristics based on a control signal ctrl_t3supplied from the logic unit 70. The spread code PN held by the codestring hold section 64 is supplied to the spread processor 63. Specificdetails of the spread code PN will be described later.

The spread processor 63 has a function (chip string acquiring function)to obtain a code string which is 12 chips long (a chip string CN2depicted in Table 1, FIG. 6 to be described later, a second chip string)by performing primary modulation (cyclic shifting or inversion to bedescribed later) on the spread code PN held by the code string holdsection 64 based on the values of symbols (information represented by atransmission signal according to the processing of the spread processor63) supplied via the switch 62. The chip string acquiring function(primary modulation process) will be described briefly below though itwill be described in greater detail later with reference to FIGS. 5through 9A, 9B.

Each of the detection pattern c1, the delimiter pattern STP, and thecontrol information c2 according to the present embodiment includes acombination of bit string associated values 0 through 15 (associated bitstrings “0000” through “1111”) and bit string unassociated values “P”and “M.” The spread code PN supplied from the spread code hold section64 is “00010010111.”

According to the primary modulation performed by the spread processor63, the values (0 through 15, P, and M) of symbols are converted intorespective corresponding chip strings CN2. Table 1 depicts specificexamples of the associated relationship between the values of symbolsand generated chip strings CN2 obtained by the chip string acquiringfunction.

TABLE 1 Transmission Values of Associated bit signal (chip stringsymbols strings Polarity Shift quantity CN2) P Unassociated Non- 01_00010010111 inverted (Reference) 0 0000 Non- +2 1_11000100101 inverted1 0001 Non- +3 1_11100010010 inverted 3 0011 Non- +4 1_01110001001inverted 2 0010 Non- +5 1_10111000100 inverted 6 0110 Non- +61_01011100010 inverted 7 0111 Non- +7 1_00101110001 inverted 5 0101 Non-+8 1_10010111000 inverted 4 0100 Non- +9 (−2) 1_01001011100 inverted MUnassociated Inverted 0 0_11101101000 (Reference) 8 1000 Inverted +20_00111011010 9 1001 Inverted +3 0_00011101101 11 1011 Inverted +40_10001110110 10 1010 Inverted +5 0_01000111011 14 1110 Inverted +60_10100011101 15 1111 Inverted +7 0_11010001110 13 1101 Inverted +80_01101000111 12 1100 Inverted +9 (−2) 0_10110100011

As depicted in Table 1, one symbol represents multiple values, and thevalue of a symbol is associated with any one of the chip strings CN2 inTable 1, which are obtained by cyclically shifting the spread code PN bya shift quantity based on the value of the symbol and non-inverting orinverting, respectively, the cyclically shifted spread code PN. Thevalue of a symbol takes one of the values (“0 through 15”), in a totalnumber (e.g., 16) indicated by a power of 2 represented by a bit stringhaving a predetermined bit length, or takes either one of the values(“P” and “M”) which are not associated with a bit string and which aredifferent from any of the values in the total number indicated by apower of 2 as described above. The former value (“0 through 15”) is usedto send the control information c2, and the latter value (“P” and “M”)is used to send the delimiter pattern STP such as a preamble or thelike.

Each of the rows of the table will be described in detail below. Thevalue “P” of a symbol is a bit string unassociated value, and isconverted into a code string including the spread code PN “00010010111”having autocorrelation characteristics with a fixed chip “1” added tothe beginning thereof. The bit string unassociated value “M” isconverted into a code string including an inverted code “11101101000”produced by inverting the polarity of the spread code PN “00010010111,”with a fixed chip “0” added to the beginning thereof.

Each of the bit string associated values 0 through 7 is converted into acode string including a code produced by cyclically shifting the spreadcode PN by a shift quantity depicted in Table 1, with “1” assigned tothe beginning thereof. For example, the value “4” of a symbol isconverted into a code string including a code produced by cyclicallyshifting the spread code PN to the right by 9 (to the left by 2), with“1” assigned to the beginning thereof. Each of the bit string associatedvalues 8 through 15 is converted into a code string including a codeproduced by cyclically shifting an inverted code “11101101000” producedby inverting the polarity of the spread code PN, by a predeterminedshift quantity based on the value of the symbol, with “0” assigned tothe beginning thereof. For example, the value “12” of a symbol isconverted into a code string including a code produced by inverting thespread code PN and cyclically shifting the inverted spread code to theright by 9 (to the left by 2), with “0” assigned to the beginningthereof.

The difference between the closest shift quantities among the shiftquantities of the bit string associated values 0 through 7 for use in acommand is 1. On the other hand, the difference between the shiftquantity of the value “P” of a symbol for use in the delimiter patternSTP such as a preamble or the like (i.e., 0), and the closest shiftquantity of the bit string associated value “2” (2 to the right) or theclosest shift quantity of the bit string associated value “4” (2 to theleft) among the bit string associated values 0 through 7, is 2, which islarger than the smallest difference among the differences between theshift quantities of the bit string associated values 0 through 7. Sincethe difference between the shift quantity (“0”) of the values “P” and“M” of symbols for use in the delimiter pattern such as a preamble orthe like and the shift quantity (+2, −2) of the values (“0,” “4” and“8,” “12”) for use in a command is thus larger than the smallestdifference between the shift quantity for a certain value used in acommand and the shift quantity for another value used in a command, theprobability that the delimiter pattern such as a preamble or the likewill be determined in error to be any of predetermined valuescorresponding to a command is reduced.

A shift quantity is determined such that the smaller the Hammingdistance is between a bit string, with which the value of a certainsymbol is associated, and a bit string, with which the value of anothersymbol is associated, the smaller the difference is between the shiftquantity for the value of the certain symbol and the shift quantity forthe value of the other symbol. The reason why a shift quantity isdetermined based on the Hamming distances between the bit strings asdepicted in Table 1, rather than simply increasing a shift quantity asthe value of a symbol increases, will be described later.

The transmitter 60 (the spread processor 63 that has acquired the chipstring CN2) may not use chip strings CN2 acquired as depicted in Table 1as a transmission signal, but may perform a process (secondarymodulation process) for generating a transmission signal by modulating acarrier signal with chip strings CN2. Although the secondary modulationprocess is not necessarily required, the secondary modulation processmay include a process for Manchester-encoding chip strings CN2.

FIGS. 3A through 3C are diagrams depicting examples of signals generatedby the spread processor 63. These examples will be described below.

FIG. 3A depicts an example in which the spread processor 63 does notperform the secondary modulation process. In this example, a chip stringCN2 generated by primary modulation directly becomes a transmissionsignal generated by the spread processor 63.

FIG. 3B depicts an example in which the spread processor 63 performsonly Manchester encoding as the secondary modulation process. In thisexample, the spread processor 63 assigns rising (positive-going) edgesto chips “1” and falling (negative-going) edges to chips “0” of aplurality of chips included in a chip string CN2, thereby acquiring aManchester-encoded chip string CN2. Alternatively, the spread processor63 may Manchester-encode a chip string CN2 by assigning falling edges tochips “1” and rising edges to chips “0.” In the example depicted in FIG.3B, the Manchester-encoded chip string CN2 becomes a transmission signalgenerated by the spread processor 63.

FIG. 3C depicts an example in which the spread processor 63 performsManchester encoding and digital modulation as the secondary modulationprocess. In this example, the spread processor 63 modulates apredetermined carrier signal with the Manchester-encoded chip stringCN2, generating a transmission signal depicted in FIG. 3C. Although atransmission signal generated according to BPSK (Binary Phase ShiftKeying) is illustrated in FIG. 3C, another digital modulating techniquemay be used. In FIG. 3C, a sine-wave signal is used as the carriersignal. However, another type of carrier signal such as arectangular-wave signal may be used.

With Manchester encoding included in the secondary modulation processcarried out by the spread processor 63, the same value does not continueover a period more than a period corresponding to one chip, as can beunderstood from FIG. 3B. By thus performing secondary modulation on atransmission signal whose spectrum is spread by the spread code PN, thetransmission signal can be sent using a desired frequency band in orderto avoid low-frequency components, for example.

Referring back to FIG. 2, the transmission signal (the first controlsignal US_c1 and the second control signal US_c2) generated by thespread processor 63 is supplied to the transmission guard section 65.The transmission guard section 65 has a function to insert a guardperiod, which is a period in which neither transmission nor reception iscarried out in order to switch between a transmitting operation and areceiving operation, between a transmission period for the first controlsignal US_c1 and the second control signal US_c2 and a reception periodRDS, according to a control signal ctrl_t4 supplied from the logic unit70.

The selecting section 40 is a switch for switching between thetransmission period in which the sensor 30 sends signals and thereception period in which the sensor 30 receives signals, under thecontrol of the logic unit 70. Specifically, the selecting section 40includes switches 44 x and 44 y and conductor selecting circuits 41 xand 41 y. Based on a control signal sTRx supplied from the logic unit70, the switch 44 x operates to connect the output terminal of thetransmitter 60 to the input terminal of the conductor selecting circuit41 x during the transmission period and to connect the output terminalof the conductor selecting circuit 41 x to the input terminal of thereceiver 50 during the reception period. Based on a control signal sTRysupplied from the logic unit 70, the switch 44 y operates to connect theoutput terminal of the transmitter 60 to the input terminal of theconductor selecting circuit 41 y during the transmission period and toconnect the output terminal of the conductor selecting circuit 41 y tothe input terminal of the receiver 50 during the reception period. Basedon a control signal selX supplied from the logic unit 70, the conductorselecting circuit 41 x operates to select one of the line-shapedelectrodes 30X and to connect the selected line-shaped electrode 30X tothe switch 44 x. Based on a control signal selY supplied from the logicunit 70, the conductor selecting circuit 41 y operates to select one ofthe line-shaped electrodes 30Y and to connect the selected line-shapedelectrode 30Y to the switch 44 y.

The receiver 50 is a circuit for detecting or receiving the positionsignal DS_pos and the data signal DS_res sent by the stylus 2 based on acontrol signal ctrl_r from the logic unit 70. Specifically, the receiver50 includes an amplifying circuit 51, a detecting circuit 52, and ananalog-to-digital (AD) converter 53.

The amplifying circuit 51 amplifies and outputs the position signalDS_pos and the data signal DS_res supplied from the selecting section40. The detecting circuit 52 is a circuit for generating a voltagecommensurate with the level of an output signal from the amplifyingcircuit 51. The AD converter 53 is a circuit for generating a digitalsignal by sampling the voltage output from the detecting circuit 52 atpredetermined time intervals. The digital data output by the ADconverter 53 are supplied to the MCU 80.

The logic unit 70 and the MCU 80 serve as a controller for controllingthe transmitter 60 and the receiver 50, etc. Specifically, the MCU 80includes a microprocessor that has a ROM and a RAM therein and operatesaccording to predetermined programs. The logic unit 70 is configured tooutput control signals described above under the control of the MCU 80.The MCU 80 is configured to derive coordinate data x, y indicating theposition of the stylus 2 based on digital data supplied from the ADconverter 53 and to output the derived coordinate data x, y to the hostprocessor 32.

FIG. 4 is a block diagram depicting functional blocks of the stylus 2.As depicted in FIG. 4, the stylus 2 includes a switching section SW, areceiver 26, a transmitter 27, and a controller 28.

The switching section SW is a switch for switching between reception Rand transmission T based on a control signal SWC from the controller 28.The switching section SW connects the electrode 21 to the receiver 26during the reception R and connects the electrode 21 to the transmitter27 during the transmission T. The switching section SW is set to thereception R in an initial state, i.e., during a pre-detection period BD(see FIG. 5) before the stylus 2 detects the first control signal US_c1.

The receiver 26 is a circuit for receiving a signal (a signal arrivingat the electrode 21) supplied from the switching section SW andobtaining the values of symbols from the transmission signal depicted inTable 1. The receiver 26 includes a demodulating circuit 26 a and acorrelating circuit 26 b. In order to reduce electric power consumption,the receiver 26 is disabled in its operation except for shortenedreception periods SRP, during the pre-detection period BD before thestylus 2 detects the sensor controller 31.

Operation of the receiver 26 will be described also with reference toFIG. 5. The receiver 26 performs a receiving operation in predeterminedperiod WPa (e.g., 2.5 msec.) to receive a first control signal US_c1 inthe shortened reception periods SRP (periods shorter than the periodsWPa, e.g., 60 μsec.), and determines whether a detection pattern c1 thatis a pattern of the values of symbols, such as “PM” or “MP,” notassociated with a bit string having a predetermined length is includedin the first control signal US_c1. The stylus 2 thus tries to detect thesensor controller 31. After having detected the sensor controller 31,the receiver 26 continues the receiving operation to detect a delimiterpattern STP. The receiver 26 receives a signal, which is detected afterthe delimiter pattern STP, as a second control signal US_c2, andperforms a process of extracting control information c2 made up ofvalues D associated with a bit string having a predetermined length.

According to the present embodiment, as described above, two successiveidentical symbol values “PP” make up the delimiter pattern STP. Thedelimiter pattern STP is thus configured because the stylus 2 mayreceive a signal from the position detector 3 via its housing, not theelectrode 21, as an antenna. In such a situation, since the circuit unit24 of the stylus 2 is supplied with signals whose positive and negativesigns are inverted, the stylus 2 is unable to receive controlinformation c2 properly. Accordingly, for detecting the delimiterpattern STP, the stylus 2 monitors not only the symbol values “PP,” butalso symbol values “MM” made up of a chip string which is produced byinverting the chip string representing the symbol values “PP.” If thestylus 2 detects the symbol values “PP,” then the stylus 2 tries toreceive control information c2 by detecting a subsequent chip string asusual. On the other hand, if the stylus 2 detects the symbol values“MM,” the stylus 2 tries to receive control information c2 by invertinga subsequent chip string in its entirety after having detected the same.In this manner, for determining whether the symbol values are invertedor non-inverted, the stylus 2 uses the first chip string, inverted ornon-inverted, as a reference, thereby allowing itself to acquire data ofthe control information c2 without making errors about deciding onpolarity inversion or non-inversion, even if a signal comes from theposition detector 3 via the housing of the stylus 2, not the electrode21, and the polarity of a signal obtained through the electrode 21 isinverted.

The demodulating circuit 26 a is a receiving circuit for generating aseries of chips by receiving a signal sent by the position detector 3.Specifically, if the position detector 3 performs Manchester encodingand digital modulation as the secondary modulation process, then thedemodulating circuit 26 a performs a process of successively acquiring aseries of chips by demodulating a signal induced on the electrode 21according to the modulating technique that the spread processor 63 ofthe position detector 63 has used to modulate the carrier signal, andsuccessively decoding the series of chips according to an invertedprocess of Manchester encoding. The demodulating circuit 26 a isconfigured to supply the decoded series of chips, chip by chip, to thecorrelating circuit 26 b. If the spread processor 36 performs neitherManchester encoding nor digital modulation, then the demodulatingcircuit 26 a directly supplies a series of chips that are successivelyreceived, chip by chip, to the correlating circuit 26 b.

The correlating circuit 26 b has a function to detect a detectionpattern c1, a delimiter pattern STP, or control information c2 includedin the series of chips supplied from the demodulating circuit 26 a byperforming a correlating process between the series of chips and aplurality of known code strings. This detecting function will bedescribed in detail later with reference to FIG. 11. If the correlatingcircuit 26 b detects a detection pattern c1, then the correlatingcircuit 26 b issues an activation signal EN to the controller 28. If thecorrelating circuit 26 b detects a delimiter pattern STP, then thecorrelating circuit 26 b outputs detected time t2 to the controller 28.If the correlating circuit 26 b detects control information c2, then thecorrelating circuit 26 b outputs the detected control information c2 tothe controller 28.

The controller 28 includes a microprocessor (MCU), and is activated whenit is supplied with the activation signal EN from the receiver 26 (i.e.,when the receiver 26 detects the detection pattern c1), and performsvarious processes. Specifically, based on the detected signal t2supplied from the receiver 26, the controller 28 generates atransmission and reception schedule for various signals (the controlinformation c2, the position signal DS_pos, and the data signal DS_res).The controller 28 performs a process of generating control signals SWCbased on the generated transmission and reception schedule and supplyingthe generated control signals SWC to the switching section SW, and aprocess of controlling a method of sending the data signal DS_res basedon control information c2 supplied from the receiver 26.

The process of controlling the method of sending the data signal DS_reswill be described in detail below. If the contents of information to besent (pen ID, a pen pressure value, and the state in which a side switchis pressed, etc.) are specified by the control information c2, then thecontroller 28 controls the contents of information to be sent to theposition detector 3 according to the specified contents. Specifically,the controller 28 generates transmission data Res including theinformation to be sent and supplies the generated transmission data Resto the transmitter 27. If the transmission timing to send the datasignal DS_res (e.g., a time slot used to send the data signal DS_res) isspecified by the control information c2, then the controller 28 controlsthe timing to supply the transmission data Res to the transmitter 27 sothat the data signal DS_res will be sent at the transmission timing.Furthermore, if the frequency used to send the data signal DS_res isspecified by the control information c2, then the controller 28 controlsa modulation circuit 27 a to be described later in order to generate acarrier signal having the specified frequency.

If the receiver 26 has not detected the detection pattern c1, i.e., ifthe receiver 26 has completed the above processes in response to theprevious activation signal EN supplied thereto, but has not yet beensupplied with a next activation signal EN, then the controller 28 maydisable the above processes (i.e., the controller 28 does not performits processes). In this fashion, the electric power consumption of thecontroller 28 can be reduced.

The transmitter 27 is a circuit for sending the position signal DS_posand the data signal DS_res, and includes a modulation circuit 27 a and avoltage boosting circuit 27 b.

The modulation circuit 27 a is a circuit for generating a carrier signal(e.g., a rectangular-wave signal) having a predetermined frequency or afrequency controlled by the controller 28, and outputting the carriersignal as it is or after modulating it under the control of thecontroller 28. When the position signal DS_pos is to be sent, themodulation circuit 27 a does not modulate the carrier signal and outputsthe carrier signal as it is. When the data signal DS_res is to be sent,the modulation circuit 27 a modulates the carrier signal withtransmission data Res supplied from the controller 28, and outputs themodulated signal obtained as a result. A digital modulating techniquesuch as PSK (Phase Shift Keying) may be described as a specificmodulating technique for modulating the carrier signal.

The voltage boosting circuit 27 b is a circuit for boosting the voltageof output signals from the modulation circuit 27 a to a certainamplitude thereby to generate the position signal DS_pos and the datasignal DS_res. The position signal DS_pos and the data signal DS_resthat have been generated by the voltage boosting circuit 27 b aresupplied via the switching section SW to the electrode 21, from whichthey are transmitted into space. The voltage boosting circuit 27 b andthe modulation circuit 27 a may be realized as a single processor.

FIG. 5 is a timing chart illustrative of a chronological sequence ofoperation of the stylus 2 and the sensor controller 31. In FIG. 5, atime axis indicated at an upper section Ts represents transmission Txand reception Rx of the stylus 2, and a time axis indicated at a lowersection Tt represents transmission Tx and reception Rx of the sensorcontroller 31.

A period up to time t0 is a period in which the stylus 2 is outside adetecting range of the sensor controller 31. In order to reduce electricpower consumption, the stylus 2 operates the receiver 26 intermittentlya plurality of times in periods WPa shorter than the successivetransmission period TCP. Specifically, in each of the periods WPa, thestylus 2 operates the receiver 26 only during the shortened receptionperiod SRP, and disables the receiver 26 for the rest of the time inWPa. The time length of the reception period SRP is set to a value thatis necessary and sufficient to receive the detection pattern c1 once.

The sensor controller 31 is configured to repeat the transmission of thefirst control signal US_c1 and the second control signal US_c2 in aperiod WP.

Specifically, as the period WP starts, the sensor controller 31 repeatsthe transmission of a chip string representing the detection pattern c1over the successive transmission period TCP that is longer than theperiod WPa.

As described above, the detection pattern c1 according to the presentembodiment is “PMPMPMP . . . .” The position detector 3 converts each ofthe values P and the values M that make up the detection pattern c1 intoa chip string CN2 that is 12 chips long according to the chip stringacquiring function of the spread processor 63 depicted in FIG. 2.Details will be described later.

The sensor controller 31 is configured to send a delimiter pattern STPindicating the end of the transmission of the detection pattern c1 (orthe start of the second control signal US_c2) by sending a chip stringthat represents the same symbol value P successively twice immediatelyafter the end of the successive transmission period TCP. Each value P isconverted into a chip string CN2 which is 12 bits long according to thechip string acquiring function of the spread processor 63 depicted inFIG. 2. The transmission of the first control signal US_c1 is completedat this point.

Having completed the transmission of the first control signal US_c1, thesensor controller 31 then sends a chip string representing controlinformation c2 (i.e., the second control signal US_c2). The controlinformation c2, which is sent subsequently to the delimiter pattern STP,as described above, includes information including an arbitrary bitstring representing a command. “D1,” “D2,” “D3,” . . . , and “Dn”depicted in FIG. 4 each represent a value D that is an arbitrary 4-bitbit string (“0000,” “0001,” or the like), and is converted into a chipstring CN2 which is 12 chips long according to the chip string acquiringfunction of the spread processor 63 depicted in FIG. 2.

The sensor controller 31 that has completed the transmission of thesecond control signal US_c2 provides a reception period RDS forreceiving a signal from the stylus 2. In case the stylus 2 has receivedthe first control signal US_c1 sent as described above, the stylus 2sends the position signal DS_pos in the reception period RDS. During thereception period RDS, the sensor controller 31 waits for the receptionof the position signal DS_pos thus sent.

Upon movement of the stylus 2 into the detecting range of the sensor 30at time t0 (stylus-down), the stylus 2 detects the detection pattern c1sent by the sensor controller 31 at the timing of time t1 immediatelyafter the reception period SRP positioned in the subsequently arrivingsuccessive transmission period TCP.

When the stylus 2 detects the detection pattern c1, the stylus 2generates the activation signal EN described above and subsequentlycontinues the receiving operation beyond the reception period SRP. Ifthe sensor controller 31 sends the delimiter pattern STP while thestylus 2 is performing the receiving operation, the stylus 2 detects thedelimiter pattern STP. In case the stylus 2 detects the delimiterpattern STP, it refers to time t2 at which it detects the delimiterelement STP, and generates a transmission and reception schedule for thesecond control signal US_c2, the position signal DS_pos, and the datasignal DS_res. Specifically, as depicted in FIG. 5, the stylus 2 waitsfor the reception of the second control signal US_c2 at the timing basedon time t2, then sends the position signal DS_pos, and finally sends thedata signal DS_res.

As described above, the sensor controller 31 provides the receptionperiod RDS after having sent the second control signal US_c2 and waitsfor the reception of the position signal DS_pos. Having received theposition signal DS_pos, the sensor controller 31 calculates the position(coordinate data x, y) of the stylus 2 based on how the position signalDS_pos is received by the line-shaped electrodes 30X, 30Y depicted inFIG. 2, outputs the calculated position to the host processor 32depicted in FIG. 1, provides the reception period RDS again, and waitsfor the reception of the data signal DS_res. Having received the datasignal DS_res, the sensor controller 31 extracts the transmission dataRes from the received data signal DS_res and outputs the extractedtransmission data Res to the host processor 32.

Even after having received the position signal DS_pos and the datasignal DS_res from the stylus 2, the sensor controller 31 still repeatsthe transmission of the first control signal US_c1 and the secondcontrol signal US_c2 in the same manner as before. The stylus 2 alsorepeats the above operation. The sensor controller 31 receives theposition signal DS_pos and the data signal DS_res from the stylus 2 eachtime the stylus 2 repeats the above operation, thereby calculating theposition of the stylus 2 and acquiring the transmission data Res sent bythe stylus 2.

The outline of the position detecting system 1 has been described above.The chip string acquiring function of the spread processor 63 depictedin FIG. 2 and the detecting function of the correlating circuit 26 bdepicted in FIG. 3 will be described successively in detail below. Inparticular, specific contents of the spread code PN in addition to anexample of a specific configuration of the chip string acquiringfunction of the spread processor 63 that obtains a transmission signalfrom the values of symbols depicted in Table 1 will also be described indetail below.

FIG. 6 is a block diagram depicting functional blocks of the spreadprocessor 63 depicted in FIG. 2. As depicted in FIG. 6, the spreadprocessor 63 has a control circuit 63 a, a code inversion/non-inversionswitching circuit 63 b (code string generator), a cyclic shifter 63 c(cyclically shifting unit), a shift register 63 d (chip stringgenerator), and a modulating circuit 63 e.

The code inversion/non-inversion switching circuit 63 b has a functionto generate a code string PNa (first code string) which is 11 chips longand which has autocorrelation characteristics, based on the spread codePN (second code string) which is 11 chips long and which is stored inthe code string hold section 64. Specifically, the codeinversion/non-inversion switching circuit 63 b selects either the spreadcode PN or the inverted code from the spread code PN according toinversion information II supplied from the control circuit 63 a, andgenerates a code string PNa according to the selected code string.

The spread code PN will be described in detail below. As describedabove, the spread code PN is a code string having autocorrelationcharacteristics. When correlation values between the spread code PN anda code string produced by cyclically shifting the spread code PN or itsinverted signal by an arbitrary shift quantity are calculated, a peakcorrelation value appears only at a shift quantity 0. The fact that thespread code PN has autocorrelation characteristics will be describedbelow with reference to FIG. 9. It is assumed below that the spread codePN is “00010010111.”

FIG. 9A depicts a broken-line curve that represents correlation valuesbetween the spread code PN “00010010111” and a code string produced bycyclically shifting the spread code PN by an arbitrary shift quantity.According to the broken-line curve, the correlation values at a shiftquantity “+1” are correlation values between the spread code PN“00010010111” and a code string “10001001011” produced by cyclicallyshifting the chips of the spread code PN to the right by 1. Furthermore,the correlation values at a shift quantity “−2” are correlation valuesbetween the spread code PN “00010010111” and a code string “01001011100”produced by cyclically shifting the chips of the spread code PN to theleft by 2. It should be noted that “0” is treated as “−1” in computingthe correlation value.

FIG. 9B depicts a broken-line curve that represents correlation valuesbetween the spread code PN “00010010111” and a code string produced bycyclically shifting an inverted code “11101101000” by an arbitrary shiftquantity. According to the broken-line curve, the correlation values ata shift quantity “+1” are correlation values between the spread code PN“00010010111” and a code string “01110110100” produced by cyclicallyshifting the chips of the inverted code to the right by 1. Furthermore,the correlation values at a shift quantity “−2” are correlation valuesbetween the spread code PN “00010010111” and a code string “10110100011”produced by cyclically shifting the chips of the inverted code to theleft by 2.

In either one of FIGS. 9A and 9B, a correlation value peak representedby the broken-line curve appears only at a shift quantity “0.”Therefore, when correlation values are calculated between the spreadcode PN and a code string produced by cyclically shifting the spreadcode PN or an inverted signal by an arbitrary shift quantity, since acorrelation value peak appears only at a shift quantity “0,” it can besaid that the spread code PN has autocorrelation characteristics.

Referring back to FIG. 6, the code inversion/non-inversion switchingcircuit 63 b has a function to be supplied with a fixed code NR from thecontrol circuit 63 a, and invert or not invert the fixed code NRaccording to the inversion information II supplied from the controlcircuit 63 a, thereby generating a fixed chip NRa. The fixed code NR isa code that is 1 chip long, and is represented by “1” in the exampledepicted in FIG. 6. The fixed code NR is used in order to make the floorvalue (correlation values other than the peak) of the correlation valuesof the chip string CN2 output from the shift register 63 d equal to “0.”This point will be described separately in detail later.

The cyclic shifter 63 c is a functional block for cyclically shiftingthe code string PNa generated by the code inversion/non-inversionswitching circuit 63 b by a shift quantity SA supplied from the controlcircuit 63 a, thereby generating a chip string CN1 (first chip string).The shift register 63 d is a functional block for receiving the chipstring CN1 generated by the cyclic shifter 63 c and the fixed chip NRagenerated by the code inversion/non-inversion switching circuit 63 b asparallel data, adding the received fixed chip NRa to the received chipstring CN1 to thereby generate a chip string CN2 (second chip string),and outputting the generated chip string CN2 as serial data.

FIG. 8 is a diagram illustrative of the chip string CN2 output from theshift register 63 d. A code string C1-0 depicted in FIG. 8 representsthe chip string CN2 output from the shift register 63 d if the codeinversion/non-inversion switching circuit 63 b does not perform itsinverting process and the cyclic shifter 63 c does not cyclically shiftthe supplied code string (when the shift quantity SA is “0”), andincludes the spread code PN “00010010111” with the fixed code NR “1”added to the beginning thereof. A code string C1-n is a code stringproduced by cyclically shifting the chip string CN1 part of the codestring C1-0 by a shift quantity n, and represents the chip string CN2output from the shift register 63 d if the code inversion/non-inversionswitching circuit 63 b does not perform its inverting process and thecyclic shifter 63 c cyclically shifts the supplied code string by theshift quantity n.

A code string C2-0 depicted in FIG. 8 represents the chip string CN2output from the shift register 63 d if the code inversion/non-inversionswitching circuit 63 b performs its inverting process and the cyclicshifter 63 c does not cyclically shift the supplied code string (whenthe shift quantity SA is “0”), and includes an inverted code from thecode string C1-0. A code string C2-n is a code string produced bycyclically shifting the chip string CN1 part of the code string C2-0 bya shift quantity n, and represents the chip string CN2 output from theshift register 63 d if the code inversion/non-inversion switchingcircuit 63 b performs its inverting process and the cyclic shifter 63 ccyclically shifts the supplied code string by the shift quantity n.

Referring to FIGS. 9A and 9B again, FIG. 9A depicts a solid-line curvethat represents correlation values between the code string C1-0 depictedin FIG. 8 and a code string produced by cyclically shifting a portion,except the fixed chip NRa, of the code string C1-0 by an arbitrary shiftquantity. In addition, FIG. 9B depicts a solid-line curve thatrepresents correlation values between the code string C1-0 depicted inFIG. 8 and a code string produced by cyclically shifting a portion,except the fixed chip NRa, of an inverted code (e.g., the code stringC2-0 depicted in FIG. 8) by an arbitrary shift quantity. In either oneof FIGS. 9A and 9B, a correlation value peak represented by thesolid-line curve appears only at a shift quantity “0,” as with thebroken-line curve. This holds true for all the code strings C1-n, C2-nthough not illustrated. Consequently, the stylus 2 that receives thecode strings C1-n, C2-n can store the code strings C1-n, C2-n in advanceand detect code strings C1-n, C2-n included in received chip strings bycalculating correlation values between the stored code strings C1-n,C2-n and the received chip strings. The position detecting system 1according to the present embodiment sends and receives the first controlsignal US_c1 and the second control signal US_c2, using such properties.Details of a detecting operation of the stylus 2 to detect the codestrings C1-n, C2-n will be described later.

As depicted in FIG. 9A, the floor value of the correlation values(broken-line curve) calculated with respect to the spread code PN is“−1,” whereas the floor value of the correlation values (solid-linecurve) calculated with respect to the code string C1-0 is “0.”Furthermore, as depicted in FIG. 9B, the floor value of the correlationvalues (broken-line curve) calculated with respect to the inverted codefrom the spread code PN is “+1,” whereas the floor value of thecorrelation values (solid-line curve) calculated with respect to theinverted code from the code string C1-0 is “0.” The floor value of thecorrelation values is “0” because the fixed chip NRa is placed at thebeginning of the chip string CN2, making the number of positive chipsand the number of negative chips equal to each other. Conversely,placing the fixed chip NRa at the beginning of the chip string CN2 makesthe floor value of the correlation values equal to “0.”

If the fixed chip NRa is not added to the spread code PN, then thedistance between the floor value “−1” of the correlation values and themaximum value “+11” thereof is 10. If the fixed chip NRa is added to thespread code PN, then the distance between the floor value “0” of thecorrelation values and the maximum value “+12” thereof is 12.Consequently, it can be said that decision errors on the reception sidecan be reduced by adding the fixed chip NRa to the spread code PN,making the floor value equal to “0.” The position detector 3 accordingto the present embodiment makes it possible, from this standpoint, toreduce decision errors on the stylus 2 side.

Referring back to FIG. 6, the modulating circuit 63 e carries out thesecondary modulation process for generating a transmission signalincluding the first control signal US_c1 and the second control signalUS_c2 based on the chip string CN2 generated by the shift register 63 d.The secondary modulation process has been described in detail above. Thetransmission signal generated by the modulating circuit 63 e accordingto the secondary modulation process reaches the sensor 30 via thetransmission guard section 65 and the selecting section 40 depicted inFIG. 2, and is sent through the touch surface 3 a (see FIG. 1) to thestylus 2 by the sensor 30.

The control circuit 63 a is a functional block for controlling variousparts of the spread processor 63. The functions performed by the controlcircuit 63 a include a function to generate the fixed code NR and theinversion information II and supply them to the codeinversion/non-inversion switching circuit 63 b, and a function togenerate the shift quantity SA and supply it to the cyclic shifter 63 c.

FIG. 7 is a block diagram depicting functional blocks of the controlcircuit 63 a for generating the fixed code NR and the inversioninformation II. As depicted in FIG. 7, the control circuit 63 afunctionally has an input acceptor 100, an inversion informationdetermining section 101, a shift quantity determining section 102, ashift quantity/inversion information storage unit 103, and an outputselecting section 104.

The input acceptor 100 is a functional block for accepting the values P,M, D that make up the detection pattern c1, the delimiter pattern STP,and the control information c2 input from the switch 62 depicted in FIG.2. If the input acceptor 100 accepts the value P or the value M inputwhich is not associated with a particular bit string, then it suppliesthe accepted value to the output selecting section 104. If the inputacceptor 100 accepts the value D (which is 4 bits long here)representing a bit string, it supplies the most significant bit thereofas an inversion information indicator bit IIIB (a second bit stringwhich is 1 bit long that is to be sent to the stylus 2) to the inversioninformation determining section 101, and supplies the rest (three bits)as a shift quantity indicator bit string SAIB (a first bit string whichhas a predetermined bit length of 2 bits or more that is to be sent tothe stylus 2) to the shift quantity determining section 102.

The inversion information determining section 101 is a functional blockfor determining first inversion information II1 based on the inversioninformation indicator bit IIIB supplied from the input acceptor 100.Specifically, the inversion information determining section 101 storestherein an inversion allocation table 101 a depicted in Table 2 below,and determines first inversion information II1 according to theinversion allocation table 101 a. The first inversion information II1thus determined is supplied to the output selecting section 104.

TABLE 2 Inversion information First inversion information indicator bitIIIB II1 0 Not to be inverted 1 To be inverted

The shift quantity determining section 102 is a functional block fordetermining a first shift quantity SA1 based on the shift quantityindicator bit string SAIB supplied from the input acceptor 100.Specifically, the shift quantity determining section 102 stores thereina shift quantity allocation table 102 a depicted in Table 3 below, anddetermines a first shift quantity SA1 according to the shift quantityallocation table 102 a. The first shift quantity SA1 thus determined issupplied to the output selecting section 104.

TABLE 3 Shift quantity indicator bit First shift string SAIB quantitySA1 000 2 001 3 011 4 010 5 110 6 111 7 101 8 100 9

As can be understood from Table 3, the shift quantity determiningsection 102 according to the present embodiment first determines a value“2” as the first shift quantity SA1 for a bit string “000”(predetermined reference bit string). The value represented by “2” is avalue produced by adding a predetermined value (=2) to a second shiftquantity SA2 (=0) to be described later. With respect to each of aplurality of bit strings produced by successively incrementing the bitstring “000” according to a predetermined criterion, values obtained byadding the number of incrementing to the first shift quantity SA1 (=2)determined for the bit string “000” are determined as the first shiftquantity SA1. The predetermined criterion is given as the fact that theHamming distance between a bit string to be incremented and a bit stringthat has been incremented is 1. The significance of why the abovecriterion is employed will be described later.

For example, a bit string that is obtained by incrementing the bitstring “000” three times according to the above criterion is “010,” anda first shift quantity SA1 to be allocated to the bit string “010” is“5” (=2+3) obtained by adding the number (=3) of incrementing to thefirst shift quantity SA1 (=2) determined for the bit string “000.”

The shift quantity/inversion information storage unit 103 stores thereinrespective values of second inversion information II2, a second shiftquantity SA2, third inversion information II3, and a third shiftquantity SA3. Specifically, the shift quantity/inversion informationstorage unit 103 stores therein “not to be inverted” as the secondinversion information II2, “0” as the second shift quantity SA2, “to beinverted” as the third inversion information II3, and “0” as the thirdshift quantity SA3.

In response to the value P supplied from the input acceptor 100, theoutput selecting section 104 supplies the second inversion informationII2 and the second shift quantity SA2 stored in the shiftquantity/inversion information storage unit 103 respectively as theinversion information II and the shift quantity SA to the codeinversion/non-inversion switching circuit 63 b and the cyclic shifter 63c, respectively, depicted in FIG. 6. The shift register 63 d depicted inFIG. 6 now outputs the code string C1-0 depicted in FIG. 8 as the chipstring CN2. Moreover, in response to the value M supplied from the inputacceptor 100, the output selecting section 104 supplies the thirdinversion information II3 and the third shift quantity SA3 stored in theshift quantity/inversion information storage unit 103 respectively asthe inversion information II and the shift quantity SA to the codeinversion/non-inversion switching circuit 63 b and the cyclic shifter 63c, respectively, depicted in FIG. 6. The shift register 63 d depicted inFIG. 6 now outputs the code string C2-0 depicted in FIG. 8 as the chipstring CN2.

In response to neither of the values P, M supplied from the inputacceptor 100 (i.e., in response to the value D input from the inputacceptor 100), the output selecting section 104 supplies the firstinversion information II1 determined by the inversion informationdetermining section 101 as the inversion information II to the codeinversion/non-inversion switching circuit 63 b depicted in FIG. 6, andalso supplies the first shift quantity SA1 determined by the shiftquantity determining section 102 as the shift quantity SA to the cyclicshifter 63 c depicted in FIG. 6. The shift register 63 d depicted inFIG. 6 now outputs either one of the code strings C1-2 through C1-9 andC2-2 through C2-9 depicted in FIG. 8 as the chip string CN2. Morespecifically, if the inversion information II represents “not to beinverted,” then the shift register 63 d outputs a code string C1-SA, andif the inversion information II represents “to be inverted,” then theshift register 63 d outputs a code string C2-SA. FIG. 8 also illustratesan associated relationship between the bit string that is 4 bits longwhich is accepted by the input acceptor 100 and the chip string CN2output by the shift register 63 d. For example, if the bit stringaccepted by the input acceptor 100 is “0010,” then the chip string CN2output by the shift register 63 d is the code string C1-5, i.e.,“110111000100.” Furthermore, if the bit string accepted by the inputacceptor 100 is “1010,” then the chip string CN2 output by the shiftregister 63 d is the code string C2-5, i.e., “001000111011.”

In this manner, the transmitter 60 can generate a transmission signalincluding a chip string CN2 that is obtained by cyclically shifting thespread code PN having autocorrelation characteristics by the shiftquantity based on the value of a symbol to be sent, and inverting (ornon-inverting) the cyclically shifted spread code PN, if necessary, asdepicted in Table 1 above. As long as a chip string CN2 can be obtained,the order of the cyclically shifting process and the inverting ornon-inverting process carried out by the transmitter 60 does not matter.Alternatively, the transmitter 60 may store the association between thevalues of symbols and chip strings CN2 or transmission signals includingthem as depicted in Table 1 in a memory, and may read and send a chipstring CN2 stored in the memory each time the value of a symbol is inputthereto.

FIG. 10 is a diagram depicting an example of the second control signalUS_c2 that the position detector 3 sends to the stylus 2. In the exampledepicted in FIG. 10, the position detector 3 sends the value Psuccessively twice to form the delimiter pattern STP as a preamble, andthereafter sends three values D1 “0” (0b0000), D2 “8” (0b1000), D3 “6”(0b0110) as the control information c2. For sending the value P, theshift register 63 d outputs the code string C1-0, i.e., “100010010111,”depicted in FIG. 8 as the chip string CN2. For sending the controlinformation c2, the shift register 63 d generates a chip string CN2 foreach of the 4-bit values D1, D2, D3. For the first 4-bit value D1, sincethe corresponding bit string is “0000,” the shift register 63 dgenerates the code string C1-2, i.e., “111000100101,” depicted in FIG. 8as the chip string CN2. For the next 4-bit bit string D2, since itscontent is “1000,” the shift register 63 d generates the code stringC2-2, i.e., “000111011010,” depicted in FIG. 8 as the chip string CN2.For the last 4-bit bit string D3, since its content is “0110,” the shiftregister 63 d generates the code string C1-6, i.e., “101011100010,”depicted in FIG. 8 as the chip string CN2.

Part or all of the bit string D3 that is the last one value (4-bitvalue) of the control information c2, for example, may include anerror-correcting code calculated based on the bit strings D1 and D2,which precede the bit string D3. In this manner, the stylus 2 on thereception side is able to detect or correct a bit error generated in thebit strings D1 and D2 using the error-correcting code.

The criterion “that the Hamming distance between a bit string to beincremented and a bit string that has been incremented is 1” used as thepredetermined criterion for determining the first shift quantity SA1will be described below. When the stylus 2 receives a chip string CN2,it may receive a chip string CN2 with the shift quantity shifted by 1.For example, such a case happens when although the position detector 3has sent the code string C1-6 depicted in FIG. 8, the stylus 2determines that it has received the code string C1-7. In order tocorrect the erroneous decision with the above error-correcting code, itis desirable that the difference between the bit string represented bythe code string C1-6 and the bit string represented by the code stringC1-7 should be as small as possible. According to the presentembodiment, inasmuch as the above predetermined criterion is employed,the bit string represented by the code string C1-6 is “0110” and the bitstring represented by the code string C1-7 is “0111,” and the differencebetween them is only one bit. Even if an erroneous decision is made, itis only one bit different, and the error can be corrected by anerror-correcting code capable of correcting one bit which is sent withthe transmission of the command. By thus employing the criterion “thatthe Hamming distance between a bit string to be incremented and a bitstring that has been incremented is 1” and adding the error-correctingcode, therefore, signals can be sent which are robust against erroneousdecisions about shift quantities.

FIG. 11 is a block diagram depicting functional blocks of thecorrelating circuit 26 b depicted in FIG. 4. As depicted in FIG. 11, thecorrelating circuit 26 b has a shift register 110, a code string storageunit 111, a detection pattern detector 112, a delimiter pattern detector113 (preamble detector), a bit string detector 114, and a commandrestorer 115.

The shift register 110 includes a first-in, first-out register foraccepting a series of chips acquired by the demodulating circuit 26 a,bit by bit, and is configured to be able to accumulate 12 chips. Whenmore than 12 chips are input to the shift register 110, older ones aresuccessively deleted from the shift register 110.

The code string storage unit 111 stores a plurality of code strings thatare obtained by cyclically shifting a predetermined code string havingautocorrelation characteristics by arbitrary shift quantities.Specifically, code strings that need to be stored in the code stringstorage unit 111 are all code strings that can possibly be sent by theposition detector 3. Therefore, the code string storage unit 111according to the present embodiment may store the code strings C1-0,C1-2 through C1-9, C2-0, and C2-2 through C2-9 depicted in FIG. 8.

The detection pattern detector 112, which has an internal timer (notdepicted), is a functional block for performing a detecting operation todetect the detection pattern c1 included in a series of chips outputfrom the demodulating circuit 26 a in case the timer indicates that thepresent time is within a reception period SRP depicted in FIG. 5. In thedetecting operation, specifically, each time a new chip is input to theshift register 110, the detection pattern detector 112 calculatescorrelation values between the chip string temporarily accumulated inthe shift register 110 and those code strings which correspond to thevalues P, M of the detection pattern c1, among the code strings storedin the code string storage unit 111, specifically, the code string C1-0and the code string C2-0. Then, when the correlation value with the codestring C1-0 represents a peak value, the detection pattern detector 112determines that it has detected the value P, and when the correlationvalue with the code string C2-0 represents a peak value, the detectionpattern detector 112 determines that it has detected the value M. Inresponse to alternately detecting the value P and the value Msuccessively a predetermined number of times, the detection patterndetector 112 determines that it has detected the detection pattern c1,and issues the activation signal EN described above to the controller28.

The delimiter pattern detector 113 is a functional block for starting adetecting operation to detect the delimiter pattern STP (preamble)included in a series of chips output from the demodulating circuit 26 ain response to the detection of the detection pattern c1 by thedetection pattern detector 112. In the detecting operation,specifically, each time a new chip is input to the shift register 110,the delimiter pattern detector 113 calculates a correlation valuebetween the chip string temporarily accumulated in the shift register110 and the code string which corresponds to the value P of thedelimiter pattern STP, among the code strings stored in the code stringstorage unit 111, specifically, the code string C1-0. Then, when thecalculated correlation value represents a peak value, the delimiterpattern detector 113 determines that it has detected the value P. Inresponse to detecting the value P successively twice, the delimiterpattern detector 113 determines that it has detected the delimiterpattern STP, stops the detecting operation, and outputs detected time t2described above to the controller 28.

The bit string detector 114 is a functional block for performing adetecting operation to detect the value D (a bit string that is 4 bitslong) included in a series of chips output from the demodulating circuit26 a at a timing when the transmission and reception schedule generatedby the controller 28 indicates that the present time is within thereception period of the control information c2. In the detectingoperation, specifically, each time a new chip is input to the shiftregister 110, the bit string detector 114 calculates correlation valuesbetween the chip string temporarily accumulated in the shift register110 and those code strings which correspond to the value D, among thecode strings stored in the code string storage unit 111, specifically,the code string C1-2 through C1-9, C2-2 through C2-9. When any of thecalculated values represents a peak value, the bit string detector 144determines that it has detected the value D (a bit string that is 4 bitslong) corresponding to the code string that indicates the peak value.The bit string detector 144 outputs the bit string which is the detectedvalue D to the command restorer 115 each time.

The command restorer 115 is a functional block for joining bit stringssuccessively supplied from the bit string detector 114 to restore thecontrol information c2 sent by the position detector 3. The commandrestorer 115 is configured to output the restored control information c2to the controller 28. The command set by the position detector 3 is thussupplied to the controller 28.

As described above, since the position detector 3 and the stylus 2according to the present embodiment uses the cyclic shifting of codestrings in generating a chip string CN2 to be sent by the positiondetector 3, it is possible to express 2 bits or more with one codestring. Accordingly, it is possible to obtain a high bit rate at thesame chip rate, compared with the background art where only 1 bit can beexpressed by one code string.

Furthermore, because the chip string CN1 with the fixed chip NRa addedthereto is used as the chip string CN2, detection errors on thereception side are reduced, reducing the possibility that a receptionerror will occur on the stylus 2 side.

For each of a plurality of bit strings produced by successivelyincrementing a predetermined reference bit string according to apredetermined criterion, a value obtained by adding the number ofincrementing to a first shift quantity SA1 determined for the referencebit string is determined as a first shift quantity SA1, and thecriterion “that the Hamming distance between a bit string to beincremented and a bit string that has been incremented is 1” is employedas the above predetermined criterion. Consequently, even if a chipstring CN2 is received with the shift quantity shifted by 1, errorcorrection due to erroneous decisions about a shift quantity can be keptto a 1-bit error, and hence can be realized by a shortererror-correcting code.

Although the preferred embodiment of the present disclosure has beendescribed above, the present disclosure is not limited to theembodiment, but can be reduced to practice in various forms withoutdeparting from the scope thereof.

For example, in the above embodiment, 11-bit “00010010111” is used asthe spread code PN. However, any code string can be used as the spreadcode PN insofar as it has autocorrelation characteristics. Though onespread code PN is used to send the value of one symbol, a plurality of(e.g., five) identical chip strings CN2 may be included with respect tothe value of one symbol. Such a case is equivalent to the transmissionof the value of the same symbol a plurality of times (i.e., five times),and erroneous decisions about a shift quantity can further be reduced byselecting a most probable shift quantity from a plurality of shiftquantities.

Table 4, Table 5, and FIGS. 12 and 13 are illustrative of chip stringsCN2 output from the shift register 63 d depicted in FIG. 6 according toa first modification of the above embodiment.

TABLE 4 Values of Associated bit Shift Transmission signal symbolsstrings Polarity quantity (chip string CN2) P Unassociated Non- 01_000010010001101 inverted 1011110001010111 0 0000 Non- +51_101110000100100 inverted 0110110111100010 1 0001 Non- +81_010101110000100 inverted 1000110110111100 3 0011 Non- +111_100010101100001 inverted 0010001101101111 2 0010 Non- +141_111100010101100 inverted 0010010001101101 6 0110 Non- +171_10111100010101 inverted 1100001001000110 7 0111 Non- +201_110110111100010 inverted 1011100001001000 5 0101 Non- +231_000110110111100 inverted 0101011100001001 4 0100 Non- +261_001000110110111 inverted (−5) 1000101011100001

TABLE 5 Values of Associated Shift Transmission signal symbols bitstrings Polarity quantity (chip string CN2) M Unassociated Inverted 00_111101101110010 (Reference) 01000011101010000 8 1000 Inverted +50_010001111011011 1001001000011101 9 1001 Inverted +8 0_1010100011110110111001001000011 11 1011 Inverted +11 0_011101010001111 011011100100100010 1010 Inverted +14 0_000011101010001 1110110111001001 14 1110 Inverted+17 0_001000011101010 0011110110111001 15 1111 Inverted +200_001001000011101 0100011110110111 13 1101 Inverted +230_111001001000011 1010100011110110 12 1100 Inverted +260_110111001001000 (−5) 0111010100011110

According to the present modification, a bit string“0000100100011011011110001010111” that is 31 bits long is used as thespread code PN. This spread code PN has autocorrelation characteristicsas with the 11-bit spread code PN used in the above embodiment.

According to the present modification, a shift quantity allocation table102 a is configured as depicted in Table 6 below. Table 6 is differentfrom the shift quantity allocation table 102 a depicted in Table 3 inthat the first shift quantity SA1 determined for the reference bitstring “000” is “5” (a value produced by adding 5 to the second shiftquantity SA2 (=0)) rather than “2” and the number added to the firstshift quantity SA1 (=5) is not the number of incrementing itself, but anumber corresponding to the number of incrementing (specifically, “thenumber of incrementing” times 3). The values of the second inversioninformation II2 and the second shift quantity SA2 that are stored in theinversion allocation table 101 a and the shift quantity/inversioninformation storage unit 103 are the same as those indicated in theabove embodiment.

TABLE 6 Shift quantity indicator First shift bit string SAIB quantitySA1 000 5 001 8 011 11 010 14 110 17 111 20 101 23 100 26

According to the present modification, a code string C3-0 depicted inFIG. 12 corresponds to the value P, a code string C4-0 depicted in FIG.13 corresponds to the value M, and code strings C3-5, C3-8, C3-11,C3-14, C3-17, C3-20, C3-23, and C3-26 depicted in FIG. 12 and codestrings C4-5, C4-8, C4-11, C4-14, C4-17, C4-20, C4-23, and C4-26depicted in FIG. 13 correspond to bit strings that are 4 bits long. Thecode string C3-0 includes the spread code PN“0000100100011011011110001010111” with a fixed code NR“1” added to thebeginning thereof. A code string C3-n is a code string produced bycyclically shifting only part corresponding to the chip string CN1 ofthe code string C3-0 by a shift quantity n, a code string C4-0 is aninverted code from the code string C3-0, and a code string C4-n is acode string produced by cyclically shifting only part corresponding tothe chip string CN1 of the code string C4-0 by a shift quantity n.

Even though the longer spread code PN is used, it is thus possible toexpress multiple values of 2 bits or more with one transmission signalas is the case with the above embodiment. Though the bit rate is lowerto the extent that the spread code PN is now longer, since thedifference between shift quantities for adjacent code strings is larger,it is possible to reduce the possibility that the stylus 2 willerroneously determine and detect a shift quantity (the value of acorresponding symbol). For example, even if a shift quantity is detectedas +6 to the right, robust decoding can be carried out for the shiftquantity error by determining the shift quantity as a value “0” which isoriginally +5 to the right. With a shift quantity being set to an oddnumber of 3 or more in the modification, a margin of the same discretevariant can preferably be provided in determining shift quantities, forexample, by determining a shift quantity as a value “1” which isoriginally +8 to the right if the shift quantity is detected as +7 tothe right and by determining a shift quantity as a value “0” which isoriginally +5 to the right if the shift quantity is detected as +5 tothe right.

In the above modification, the difference between the closest shiftquantities among the shift quantities for the bit train associatedvalues 0 through 7 used in a command is 3. On the other hand, thedifference between a shift quantity (i.e., 0) for the symbol value “P”used in the delimiter pattern STP such as a preamble or the like and theclosest shift quantity (5 to the right) for the value “0” or the closestshift quantity (5 to the left) for the value “4” among the bit trainassociated values 0 through 7 used in a command is 5, which is largecompared with 3 that represents the difference between the shiftquantities for bit train associated values 0 through 7. Since thesmallest difference (5) among the differences between the shiftquantities based on the symbol values “P” and “M” used in the delimiterpattern STP such as a preamble or the like and the shift quantitiesbased on the values that make up a command is thus larger than thesmallest difference (3) among the differences between the shift quantitybased on one value of a command and the shift quantity based on anothervalue of the command, the probability that the delimiter pattern such asa preamble or the like will be determined in error as a predeterminedvalue corresponding to a command is reduced.

In the above embodiment, the demodulating circuit 26 a of the stylus 2performs an inverted process of Manchester encoding. However, eventhough the spread processor 63 of the position detector 3 carries outManchester encoding, the demodulating circuit 26 a need not perform aninverted process of Manchester encoding. A processing operation of thestylus 2 in such a modification will be described below with referenceto FIG. 14.

FIG. 14 is a block diagram depicting functional blocks of a correlatingcircuit 26 b according to a second modification of the above embodiment.As depicted in FIG. 14, the correlating circuit 26 b according to thepresent modification has a shift register 120, a Manchester encoder 121,a detection pattern detector 122, a delimiter pattern detector 123(preamble detector), and a bit string detector 124, in place of theshift register 110, the detection pattern detector 112, the delimiterpattern detector 113 (preamble detector), and the bit string detector114 depicted in FIG. 11.

The shift register 120 is different from the shift register 110according to the above embodiment, which is able to store only 12 chips,in that the shift register 120 is configured to be able to store 24chips. This is because the number of chips that are input to the shiftregister 120 for one chip string CN2 increases to 24 as the demodulatingcircuit 26 a does not perform an inverted process of Manchesterencoding.

The Manchester encoder 121 is a functional block for Manchester-encodinga code string stored in the code string storage unit 111 when the codestring is supplied to the detection pattern detector 122, the delimiterpattern detector 123, and the bit string detector 124. Therefore, thedetection pattern detector 122, the delimiter pattern detector 123, andthe bit string detector 124 are supplied with the Manchester-encodedcode string.

The detection pattern detector 122, the delimiter pattern detector 123,and the bit string detector 124 are different respectively from thedetection pattern detector 112, the delimiter pattern detector 113, andthe bit string detector 114 in that they are configured to calculatecorrelation values between a chip string that is 24 chips long which istemporarily accumulated in the shift register 120 and the code stringthat is 24 chips long which has been Manchester-encoded. The otherdetails of the detection pattern detector 122, the delimiter patterndetector 123, and the bit string detector 124 are the same as those ofthe detection pattern detector 112, the delimiter pattern detector 113,and the bit string detector 114.

A Manchester-encoded code string usually does not exhibit the cleanautocorrelation characteristics (autocorrelation characteristics whosefloor values are the same) depicted in FIGS. 9A and 9B. However, sinceits peak value can be detected, the detection pattern detector 122, thedelimiter pattern detector 123, and the bit string detector 124 are ableto detect a detection pattern c1, a delimiter pattern STP, and a bitstring that is 4 bit long, respectively, according to the above process.

In the above embodiment, it has been described that the positiondetector 3 sends the second control signal US_c2 following the firstcontrol signal US_c1, as depicted in FIG. 5. However, after having sentthe first control signal US_c1 (specifically, a chip string CN2corresponding to the delimiter pattern STP), the position detector 3 maysend the second control signal US_c2 (specifically, a chip string CN2corresponding to the control information c2) after the elapse of apredetermined time period longer than 0.

FIG. 15 is a timing chart illustrative of a chronological sequence ofoperation of a stylus 2 and a sensor controller 31 according to a thirdmodification of the above embodiment. A position detector 3 depicted inFIG. 15 is different from the position detector 3 according to the aboveembodiment in that it does not send the second control signal US_c2following the first control signal US_c1, but provides a receptionperiod RDS having a predetermined time length WT after having sent thefirst control signal US_c1, and sends the second control signal US_c2only if the position signal DS_pos is received during the receptionperiod RDS. Even though the gap is provided between the first controlsignal US_c1 and the second control signal US_c2, as long as the timelength of the gap is determined in advance, the stylus 2 can determine atransmission and reception schedule while taking the gap into account,and hence can receive the second control signal US_c2 without anyproblems.

In the above embodiment, one chip string CN2 is assigned to 4 bits.However, the number of bits that can be assigned to one chip string CN2is not limited to 4. Particularly, if long code strings as depicted inFIGS. 12 and 13 are used, one code string may represent more bits.

In the above embodiment, the detection pattern c1 and the delimiterpattern STP are represented by the dedicated code strings C1-0, C2-0.However, they may be represented by code strings which are the same ascode strings for bit strings. If the code strings C1-0, C2-0 arededicated to the detection pattern c1 and the delimiter pattern STP,then as depicted in FIG. 8, detection errors are reduced in detectingthe detection pattern c1 and the delimiter pattern STP by making thedifferences (2 in FIG. 8) between the shift quantities for the codestring C1-0 (or the code string C2-0) and the adjacent code stringsC1-1, C1-9 (or the code strings C2-1, C2-9) larger than the differences(1 in FIG. 8) between the shift quantities for the code strings C1-n (orthe code strings C2-n) (n≠1), although code strings that can be used forsending bit strings are reduced. However, using code strings which arethe same as code strings for bit strings as the delimiter pattern STP,as described above, is advantageous in that code strings that can beused for sending bit strings are increased.

In the above embodiment, a chip string CN1 with a fixed chip NRa addedthereto is used as a chip string CN2. However, if no problem arises fromnoise caused by the fact that the floor value of correlation values isnot “0,” then a chip string CN1 may be used directly as a chip stringCN2.

In the above embodiment, a chip string CN1 with a fixed chip NRa addedto the beginning thereof is used as a chip string CN2. However, a chipstring CN2 may be made up of a chip string CN1 and a fixed chip NRaadded to the tail end of the chip string CN1.

In the above embodiment, an example in which the detection pattern c1 issent before the delimiter pattern STP has been described. However, ifthe stylus 2 may perform its receiving operation continuously ratherthan intermittently, then the transmission of the detection pattern c1may be omitted. In such a case, the stylus 2 detects the positiondetector 3 by detecting the delimiter pattern STP.

In the above embodiment, the present disclosure is applied to signalsthat the position detector 3 sends to the stylus 2. However, the presentdisclosure is also applicable to signals that the stylus 2 sends to theposition detector 3.

In the above embodiment, the spread processor 63 includes the codeinversion/non-inversion switching circuit 63 b and the cyclic shifter 63c, so that code strings are inverted and cyclically shifted in thespread processor 63. However, the spread processor 63 may be configuredsuch that it stores the values of symbols that may possibly be input tothe control circuit 63 a and chip strings CN2 to be output in anassociated relationship in a storage area, and generates a chip stringCN2 corresponding to the value of an input symbol by reading it from thestorage area.

DESCRIPTION OF REFERENCE SYMBOLS

1 Position detecting system

2 Stylus

3 Position detector

3 a Touch surface

20 Core

20 a Distal end

21 Electrode

23 Pen pressure detection sensor

24 Circuit unit

25 Power supply

26 Receiver

26 a Demodulating circuit

26 b Correlating circuit

27 Transmitter

27 a Modulation circuit

27 b Voltage boosting circuit

28 Controller

30 Sensor

30X, 30Y Line-shaped electrode

31 Sensor controller

32 Host processor

40 Selecting section

41 x, 41 y Conductor selecting circuit

44 x, 44 y Switch

50 Receiver

51 Amplifying circuit

52 Detecting circuit

53 Analog-to-digital converter

60 Transmitter

61 Control signal supply section

62 Switch

63 Spread processor

63 a Control circuit

63 b Code inversion/non-inversion switching circuit

63 c Cyclic shifter

63 d Shift register

63 e Modulating circuit

64 Code string hold section

65 Transmission guard section

70 Logic unit

80 MCU

100 Input acceptor

101 Inversion information determining section

101 a Inversion allocation table

102 Shift quantity determining section

102 a Shift quantity allocation table

103 Shift quantity/inversion information storage unit

104 Output selecting section

110 Shift register

111 Code string storage unit

112 Detection pattern detector

113 Delimiter pattern detector

114 Bit string detector

115 Command restorer

120 Shift register

121 Manchester encoder

122 Detection pattern detector

123 Delimiter pattern detector

124 Bit string detector

c1 Detection pattern

c2 Control information

CN1, CN2 Chip string

DS Downlink signal

DS_pos Position signal

DS_resData signal

EN Activation signal

II Inversion information

II1 First inversion information

II2 Second inversion information

IIIB Inversion information indicator bit

NR Fixed code

NRa Fixed chip

PN Spread code

PNa Code string

SA Shift quantity

SA1 First shift quantity

SA2 Second shift quantity

SAIB Shift quantity indicator bit string

STP Delimiter pattern

SW Switching section

US Uplink signal

US_c1 First control signal

US_c2 Second control signal

1. A position indicator configured to be able to receive a signal sentby a sensor controller through a position detector having a touchsurface, the position indicator comprising: a receiver which, inoperation, receives a signal, demodulates a value of a symbol includedin the signal based on a cyclic shift quantity for a code string whichhas autocorrelation characteristics and which is included in the signal,and restores a sent command based on the demodulated value of thesymbol; and a controller coupled to the receiver and which, inoperation, controls transmission of a signal to the sensor controller inresponse to the command.
 2. The position indicator according to claim 1,wherein the symbol takes multiple values, and the receiver demodulatesany one of the multiple values based on the shift quantity.
 3. Theposition indicator according to claim 2, wherein the symbol takesmultiple values, and the receiver demodulates any one of the multiplevalues based on the shift quantity and non-inversion and inversion ofthe code string.
 4. The position indicator according to claim 2, whereinthe receiver demodulates the value of the symbol and outputs a bitstring having a predetermined bit length.
 5. The position indicatoraccording to claim 3, wherein the symbol takes any one of a total numberof values wherein the total number is indicated by a power of 2represented by a bit string having a predetermined bit length, or takesany one of 1 or more values respectively different from any of the totalnumber of values wherein the total number is indicated by the power of2, and the receiver: responsive to the symbol representing a valuedifferent from any one of the total number of values wherein the totalnumber is indicated by the power of 2, sends a signal indicatingdetection of a preamble representing a start of the command to thecontroller; and responsive to the symbol representing any one of thetotal number of values wherein the total number is indicated by thepower of 2, restores the command based on the symbol.
 6. The positionindicator according to claim 5, wherein the signal represents any one ofthe multiple values based on the shift quantity and non-inversion andinversion of the code string, and the receiver determines whether thereis non-inversion or inversion of the code string based on whether asignal corresponding to the preamble received prior to the command isnon-inverted or inverted, demodulates the symbol, and restores thecommand.
 7. The position indicator according to claim 6, wherein if thesymbol represents any one of the total number of values wherein thetotal number is indicated by the power of 2, the receiver accumulates abit string representing the demodulated symbol and performs an errorcorrection with the accumulated bit string.
 8. The position indicatoraccording to claim 1, wherein the receiver successively inputs a seriesof chips generated by receiving the signal to a first-in, first-outshift register, and each time a chip is input, calculates correlationvalues between a chip string temporarily accumulated in the shiftregister and a plurality of code strings produced by cyclically shiftinga predetermined code string having autocorrelation characteristics by ashift quantity, thereby demodulating the value of the symbol associatedwith the series of chips.
 9. The position indicator according to claim8, wherein a correlation value between the chip string temporarilyaccumulated in the shift register and the predetermined code string iscalculated, thereby detecting a preamble included in the series ofchips, and if the preamble is detected, correlation values between thechip string temporarily accumulated in the shift register and theplurality of code strings are calculated, thereby detecting a bit stringincluded in the series of chips.